1. Understanding big accidents

2. NASA's failing grade

3. The blame game

4. Accidents: Normal?

5. Holey-headed reactor

The Davis-Besse nuclear reactor is owned by FirstEnergy, also implicated in the blackout of 2003. With a major hole in its head, Davis-Besse has been idle for 19 months. Photo: Ottawa County Emergency Management.

In a pressurized water reactor, like Davis-Besse, high-pressure water transfers heat. At Davis-Besse, water leaking from inside the reactor vessel caused severe corrosion (arrow) in the reactor head. The consequences of a major leak are uncertain, but the Nuclear Regulatory Commission didn't want to find out. Photo: U.S. Nuclear Regulatory Commission

A reactor with "a hole in its head"
Investigations into the recent blackout have pointed to problems early in the day on Ohio transmission lines owned by FirstEnergy Corp. As The Why Files goes to press, we read that problems surfaced even earlier at an Indiana plant.

Curiously, FirstEnergy also owns the troubled Davis-Besse nuclear plant, which has been idle for more than 570 days running -- longer, even, than the plant's previous record, 565 days.

Davis-Besse has, in technical terms, a hole in the head left by the corrosion of almost six inches of solid steel. When the reactor was finally shut down, the weakest link in the highly pressurized reactor vessel was a 3/16th-inch stainless-steel liner.

And while Davis-Besse was not, technically, an accident because it did shut down safely, one way to learn about accidents is to examine near-misses, AKA accidents-waiting-to-happen.

The immediate cause of the corrosion was a leak of acidic water from inside the reactor. But that was no surprise, says Vicki Bier, a nuclear-safety specialist at the University of Wisconsin-Madison. Corrosion "was a known problem -- plants were required to have a corrosion control program, and Davis had one like everyone else."

Reacting in the nick of time
An accident was averted due more to luck than to the corrosion control program, says Bier, who sees plenty of symptoms of those familiar culture problems at Davis-Besse:

The context: Similar reactors don't have the same holes.

The time scale: "Corrosion is a slow problem that went on for many years, with many people involved in the whole inspection process," Bier says. "It was not a one-time mistake."

The failed fix: Instead of inspecting for corrosion, Bier says, "They would blast the reactor head with a high-pressure hose ... and say they had done the corrosion program... they went through the motions and checked it off their list."

Unfortunately, the corrosion was hidden by deposits of boric acid that had leaked from the reactor vessel, and the reactor had to be shut down for safety violations. As we write, a replacement reactor head is being installed.

Don't make the mistake of ignoring our accidental bibliography...

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